How does the law of conservation of mass apply to the reaction: Mg + 2HCl → H2 + MgCl2?

• A. The law does not apply because the reaction produces a gas that escapes.
• B. The mass of the products is greater than the mass of the reactants because a gas is produced.
• C. The total mass of reactants (Mg and HCl) is equal to the total mass of products (H2 and MgCl2).
• D. The mass of the reactants is less than the mass of the products due to the formation of MgCl2.

Answer: (C)

Verified step by step guidance

1. Recall the law of conservation of mass, which states that mass cannot be created or destroyed in a chemical reaction; it only changes form.
2. Identify the reactants and products in the given reaction: reactants are Mg and HCl, products are H2 and MgCl2.
3. Understand that even though a gas (H2) is produced and may escape, the total mass of all products (including the gas) must equal the total mass of the reactants before the reaction.
4. Recognize that the formation of MgCl2 from Mg and HCl involves rearrangement of atoms, not creation or loss of mass.
5. Conclude that the total mass of reactants equals the total mass of products, demonstrating the law of conservation of mass applies to this reaction.